With the constantly improving quality of color photocopies and printings and in an attempt to protect security documents such as banknotes, value documents or cards, transportation tickets or cards, tax banderols, and product labels that have no reproduceable effects against counterfeiting, falsifying or illegal reproduction, it has been the conventional practice to incorporate various security measures in these documents. Typical examples of security measures include security threads, windows, fibers, planchettes, foils, decals, holograms, watermarks, security inks comprising optically variable pigments, magnetic or magnetizable thin-film interference pigments, interference-coated particles, thermochromic pigments, photochromic pigments, luminescent, infrared-absorbing, ultraviolet-absorbing or magnetic compounds. In addition to those security features, security documents often carry a tactilely-detectable or feelable surface profile pattern. In addition to the fact that tactile features cannot be imitated by copying machines, they have the further advantage that visually impaired people might use them as a distinguishing and identification feature.
Tactile patterns and features have been produced using different technologies including intaglio printing, inkjet printing and screen printing.
Intaglio printing is used in the field of security documents, in particular banknotes, and confers the well-known and recognizable relief features, in particular the unmistakable touch feeling, to a printed document. Intaglio printing has been used to print tactile features for visually impaired persons, e.g., in EP 1 525 993 A1 and U.S. Pat. No. 7,357,077 B2. U.S. Pat. No. 7,618,066 B2 discloses a printed carrier having a printed surface and at least one printed partial surface enclosed thereby, both surfaces being printed by an intaglio process and contrasting visually in terms of brightness, for example due to an ink layer of varying thickness. In addition to the contrasting effect, both surfaces are said to be distinguishable with the sense of touch, i.e. tactilely. The disclosed data carrier comprising the surfaces is printed with the same ink but in different thickness.
US-2005/0115425 A1 discloses a data carrier printed by an intaglio process exhibiting a tactile feature. It is further disclosed that images printed by rotogravure (also described in the art as heliogravure) have no tactility due to the lack of viscosity of the ink and the low contact pressure during the printing process, thus preventing relief formation.
Inkjet printing has been used to print tactile features. U.S. Pat. No. 6,644,763 B1 and US-2009/0155483 A1 disclose inkjet printing methods for creating raised effects by applying a light curable adhesive or ink on a substrate. EP-1 676 715 A1 discloses a data carrier with a tactile feature applied by an inkjet printing process; the tactile feature may contain dyes or pigments so as to allow visual inspection and/or automated inspection. WO 2010/149476 A1 discloses a security element comprising a data consisting of a first region having a first color T1 and at least a second region having a second color T2 different from T1, wherein both regions are differentially covered, in particular by an inkjet printing process, with a transparent or translucent material so as to form a raised tactile element.
WO 2010/071993 A1 discloses a method for making tactile patterns on a substrate by applying by screen printing or inkjet printing a UV-curable deposit material having a viscosity in the range of 2000 to 25000 cP at 25° C. onto said substrate. The disclosed UV-curable deposit material, which may further comprise a taggant so as to increase the level of security of a security document comprising said material, is said to exhibit high adhesion due to the presence of a low viscosity acrylate component, an adhesion-promoting acid acrylate and a rheological adsorbing additive such as fumed silica or precipitated gel silica. WO 2010/071956 A1 and WO 2010/071992 A1 disclose a method for printing a tactile mark on a substrate comprising a step of screen printing a UV-curable ink deposit and curing said ink, and a step of intaglio calendering or printing so as to form protrusions in the substrate on the opposite side of the ink deposit.
Alternatively, a method of imparting a tactile effect by modifying the substrate itself has been developed. EP 0 687 771 A2 discloses a security paper carrying an intricate tactile surface profile pattern which has been imparted to the paper during the manufacture by using a nip. A fluorescent ink might be applied on the paper carrying the tactile pattern. However, the freedom to change the design of the tactile pattern from one process to another one is limited and it requires the alignment and/or registration of the fluorescent ink on the tactile feature, which might be tedious and time-consuming.
Alternatively, several systems include the use of particles to impart or create a tactile effect. DE 102006012329 A1 discloses inks for flexo and offset printing comprising heat and infrared expandable microspheres and infrared absorber for the production of tactile effect. US-2010/0002303 A1 discloses a security device comprising at least one zone having an interference effect and at least one tactile recognition element located in the same region. The tactile recognition element comprises particles partially incorporated into the zone having an interference effect. Consequently, the tactile effect as a security feature arises from particles sticking out the zone having the interference effect. US-2010/0219626 A1 discloses a security sheet including an iridescent security mark comprising iridescent pigments, wherein said mark may include a tactile-effect element constituted by a polyurethane (PU), in particular PU microspheres or PU in an aqueous dispersion of PU (latex) or by the iridescent pigments. US-2011/0049865 A1 discloses a security document comprising a security feature having an inherent tactile nature, said security feature comprising a printed layer with particles protruding at least ten μm (microns) therefrom and in an amount of at least three particles per mm2 of the layer. Due to the inherent tactile nature of the security feature, it is disclosed that any technique including screen, lithography, letterpress, flexo, gravure and or intaglio printing might be used. The disclosed security feature could be provided with both human and machine-readable feature.
However, systems including the use of particles to create a tactile effect might have drawbacks including for example a reduction of the color strength of the printed document and a poor scratch and scuff resistance resulting in the loss of the tactile feature upon use and time.
WO 2011/001200 A1 discloses a packaging for consumer goods having a discontinuous tactile coating. The discontinuous tactile coating is formed by applying, such as for example by gravure, offset, flexo, lithographic or screen printing, one or more varnishes or tinted varnishes to the outer surface of the packaging.
As described hereabove, several solutions have been developed to produce tactile pattern on security documents; however, these solutions may suffer from drawbacks that have been cited. Therefore, a need remains for methods for manufacturing a security document combining tactility and a machine detectable or machine readable security feature while highly increasing resistance to counterfeiting and illegal reproduction and maintaining an easy and economic manufacturing process.